1. Field of Invention
This invention relates to immersion-type heaters for installation in an appropriate receptacle containing a liquid medium to be heated by the heater. Temperature of the liquid medium is controlled by sensing the temperature of heating elements of the heater and selectively closing and opening circuitry connecting the heater to a power source while at the same time the heater is protected from destructive self-generated temperatures.
2. Description of the Prior Art
Heretofore, immersion-type heaters for use within a receptacle to heat a contained liquid within that receptacle used sensing means either to control the temperature of the liquid only or to protect the heater from reaching excessive sheath temperatures only, but not both simultaneously.
Prior sensing of excessive temperatures (caused by either low liquid level, excessive mineral deposit accumulations, or "coking" of oil-base liquids) was accomplished with the sensor extending through the mounting means into the liquid medium. This required removal of the heater (after draining the liquid medium from the tank) to replace a defective or damaged sensor.